This application is concerned with the pre- and postharvest inhibition of remobilisation of storage compounds. Especially, the application describes the prevention of sprouting, especially in vegetatively propagated plants by transforming them with recombinant DNA and a method to restore sprouting in these lines.
In traditional breeding as well as in agricultural genetic engineering the major goal is to obtain crops with a high yield, which generally means that the goal has been to increase storage of the plant in the organs of the plant that are used for storage, such as the tubers in potato, the taproot in sugarbeet, and the leaves in leafy crops such as lettuce. However, other processes in plants, such as flowering and or sprouting, often give a yield penalty.
Sprouting normally can be inhibited by cold storage at very low temperatures (slightly above freezing). Cold storage is not only expensive, but also inflicts deleterious effects upon storage organs, which render them unsuitable for further processing or result in yield losses of commercial products as starch. For example when potato tubers are subjected to cold temperatures, they convert starch to reducing sugars, a phenomenon known as xe2x80x98cold sweeteningxe2x80x99. The development of reducing sugars is very undesirable because during baking and frying e.g. the Maillard reaction occurs that results in undesired browning.
To prevent cold sweetening potatoes can be stored at higher temperatures, but this results in undesired sprouting. Amongst others, chlorpropham (CIPC) is used by the industry to control tuber sprouting. Although CIPC has been used effectively, it still is considered as an undesirable chemical treatment. All around the world, there is an increasing emphasis on replacing chemical control agents with biological control mechanisms that are safe and more environmentally acceptable.
When considering a genetic approach to inhibit sprouting, it must also be considered that for the development of seed-potatoes sprouting is a desired property, and that thus a mechanism should be at hand which enables seed-potato production but which prevents sprouting in potatoes cultured for consumption or further processing.
This invention comprises a method to inhibit pre- and postharvest remobilisation of storage compounds. More specifically, the invention comprises a method to prevent sprouting of a plant part by transforming the plant or its ancestor with a recombinant DNA capable of expression of a protein, characterized in that the protein is trehalose phosphate synthase (TPS). More specifically the recombinant DNA comprising the gene coding for TPS is of bacterial, fungal, animal, plant or human origin, preferably derived from Escherichia coli. In another embodiment the invention comprises a method to induce sprouting in a plant by providing said plant with recombinant DNA coding for TPS flanked by target sites of a site-specific recombinase and removing the recombinant DNA coding for TPS by providing said plant either through transformation with a gene coding for the corresponding recombinase or through crossing with a plant capable of expressing said recombinase.
Still another embodiment of the invention comprises a method to induce sprouting in a plant by providing a plant with recombinant DNA coding for TPS and subsequently or simultaneously transforming it with a recombinant DNA which comprises a gene coding for a molecule that can neutralize the effect of TPS under control of an inducible promoter and forcing expression of the neutralizing molecule by induction of the inducible promoter. An example of such a neutralizing molecule is trehalose phosphate phosphatase (TPP) or the product of the antisense TPS gene.
Another embodiment of the invention is formed by removing the inhibition of pre- and post-harvest mobilisation of storage compounds by external treatment with compounds that neutralize the inhibitory effect of the expression of the TPS gene. Preferably this is accomplished by applying gibberellic acid. Still another embodiment of the invention is to restore sprouting by wounding.
A further object of the invention is a method to induce sprouting in a plant by providing a plant with recombinant DNA coding for TPS and subsequently or simultaneously transforming it with a recombinant DNA which comprises a gene coding a suppressor under control of an inducible promoter, said suppressor capable of suppressing expression of the TPS and forcing expression of the suppressor by induction of the inducible promoter.
Also the invention provides for plants made by any of the above mentioned methods, specifically vegetatively propagated plants and more specifically potato and onion.
Further the gene coding for TPS can be placed under control of a specific promoter, such as the patatin promoter, which specifically gives expression in the tuber of the potato plant.
Another embodiment of the invention is the inhibition of the catabolism of inulin in chicory, the inhibition of sucrose catabolism in sugarbeet and the inhibition of starch degradation in potato.